Revert of Temporarily enable PlzNavigate to see perf bot results.

content/public/common/browser_side_navigation_policy.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/public/common/browser_side_navigation_policy.h"
 
 #include "base/command_line.h"
 #include "content/public/common/content_switches.h"
 
 namespace content {
 
 bool IsBrowserSideNavigationEnabled() {
-  return true;
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableBrowserSideNavigation);
 }
 
 }  // namespace content